Method and apparatus for crystallizing semiconductor with laser beams

ABSTRACT

Laser beams emitted by a plurality of laser sources are divided into a plurality of sub-beams, which are irradiated onto selected portions of an amorphous semiconductor on a substrate to crystallize the amorphous semiconductor. A difference in diverging angles between the laser beams is corrected by a beam expander. The apparatus includes a sub-beam selective irradiating system including a sub-beam dividing assembly and a sub-beam focussing assembly. Also, the apparatus includes laser sources, a focussing optical system, and a combining optical system. A stage for supporting a substrate includes a plurality of first stage members, a second stage member disposed above the first stage members, and a third stage member  38 C, rotatably disposed above the second stage to support an amorphous semiconductor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and an apparatus forcrystallizing a semiconductor.

2. Description of the Related Art

A liquid crystal display device includes an active matrix drive circuitwhich includes TFTs. Also, a system liquid crystal display deviceincludes an electronic circuit including TFTs in the peripheral regionsaround the display region. Low-temperature polysilicon is suitable forforming TFTs for the liquid crystal display device and TFTs for theperipheral region of the system liquid crystal display device. Also,low-temperature polysilicon is applied to pixel driving TFTs for anorganic EL display, an electronic circuit for the peripheral region ofthe organic EL display and the like. The present invention relates to amethod and an apparatus for crystallizing a semiconductor, using a CWlaser (continuous wave laser), for producing TFTs with low-temperaturepolysilicon.

In order to form TFTs of the liquid crystal display device withlow-temperature polysilicon, in the prior art, an amorphous siliconlayer is formed on a glass substrate, and the amorphous silicon layer onthe glass substrate is irradiated by an excimer pulse laser tocrystallize the amorphous silicon. Recently, a crystallization methodhas been developed wherein the amorphous silicon layer on the glasssubstrate is irradiated by a CW solid laser to crystallize the amorphoussilicon.

In crystallization of silicon by means of the excimer pulse laser,mobility is in the order of 150 to 300 (cm²/Vs) but, on the other band,in crystallization of silicon by means of the CW laser, mobility in theorder of 400 to 600 (cm²/Vs) can be realized, this being particularlyadvantageous in forming TFTs for electronic circuits in the peripheralregion of the system liquid crystal display device.

In crystallizing silicon, the silicon layer is scanned by a laser beam.In this case, the substrate having the silicon layer is mounted on amovable stage, and the scanning is-performed while the silicon layer ismoved with respect to the fixed laser beam. As shown in FIG. 19, in theexcimer pulse laser scanning, scanning can be performed with a laserbeam having, for example, a beam spot “X” of 27.5 mm×0.4 mm, and thearea scan speed is 16.5 cm²/s when the beam width is 27.5 mm and thescan speed is 6 mm/s.

On the other hand, as shown in FIG. 20, in the CW solid laser scanning,scanning can be performed with a beam spot “Y” of, for example, 400μm×20 μm, and when scanning is performed at a scan speed of 50 cm/s, anacceptable crystallization melt width is 150 μm and the area scan speedis 0.75 cm²/s. In this manner, crystallization by means of a CW solidlaser, polysilicon of excellent quality can be obtained but there is theproblem that the throughput is low. Also, it is possible to performscanning at the scan speed of 2 m/s, in which case the area scan speedis 5 cm²/s. However, the mobility of the polysilicon thus attained islow.

In crystallization by means of a CW solid laser, because the output of astable CW laser is relatively low, even if the scan speed is increased,there is the problem that the area scan speed is low and throughput doesnot increase sufficiently.

In addition, if scanning is performed by the CW laser with a laser powerof, for example, 10W, the width “Y” of a beam spot of approximately 400μm, and a scan speed of 50 cm/s, an effective melt width with a beamspot of 400 μm, at which acceptable crystallization can be attained,would be 150 μm, therefore the area scan speed is 0.75 cm²/s. In thismanner, in crystallization by means of a CW solid laser, althoughpolysilicon of excellent quality can be attained, there is still theproblem of low throughput.

Further, as shown in FIG. 29, in the prior art, the movable stagesupporting the substrate having the silicon layer comprises a Y-axisstage 1, an X-axis stage 2, a rotatable stage 3, and a vacuum chuck 4.Usually, the Y-axis stage 1, which is in the lowermost position, has alarge high-speed structure that is highly mobile, and the X-axis stage2, which is positioned above the Y-axis stage 1, has a relatively smalland less mobile structure. The Y-axis stage 1 which is in the lowermostposition takes the load of all of the upper components. A substrateincluding an amorphous semiconductor is secured the vacuum chuck 4, alaser beam is irradiated onto the amorphous semiconductor while themovable stages are moved, and the amorphous semiconductor iscrystallized by being molten and hardened to form polysilicon.

With the excimer pulse laser, because the beam spot formed is relativelylarge, a high area scan speed can be achieved. However, with a CW solidlaser, because the beam spot formed is extremely small, the area scanspeed is quite low. Therefore, crystallization by means of a CW solidlaser can achieve excellent quality polysilicon, but has low throughput.

In order to improve the throughput of crystallization by means of laserscanning, the substrate having the silicon layer must be movedreciprocally at the highest possible speed. In other words, thesubstrate is accelerated from a stationary state, continues to move at aconstant speed while being scanned with laser, and thereafter isdecelerated to a stationary state. Then, the substrate is moved in theopposite direction, at which time the substrate is accelerated, moves ata constant speed, and is decelerated to a stationary state. Laserscanning is executed while this reciprocal movement of the substrate isrepeated.

In order to effectively perform high speed scanning, it is necessary toincrease the acceleration/deceleration of the high speed Y-axis stage 1.However, if the acceleration is increased, the shock of acceleration isincreased, and this shock is in proportion to the product of theacceleration and the weight of the loads supported by the stage. A largeshock will vibrate the optical system for emitting the laser beam,shifting the adjustment thereof, thus putting the optical system out offocus and moving the focusing position, making stable crystallizationunattainable.

In the prior art, because the Y-axis stage 1 which moves at high speedsupports the load of all the other stage components, and the weight ofthis load is large, the acceleration thereof cannot be sufficientlyincreased and the substrate cannot be accelerated to a high speed in ashort time.

Further, the rotatable stage 3 is used to correct dislocation of therotation position of the substrate having the silicon layer, and can berotated within the range of approximately 10 degrees. In order to rotatethe substrate having the silicon layer 90 degrees, it is necessary toremove the substrate from the vacuum chuck 4 and reattach the substrateto the vacuum chuck 4. Consequently, in the prior art, 90 degreerotation of the substrate having the silicon layer is not performed.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a method and anapparatus for crystallizing a semiconductor that can increase throughputeven in the case where a CW solid laser is used.

A method for crystallizing a semiconductor, according to the presentinvention, comprises the steps of dividing a laser beam emitted by alaser source into a plurality of sub-beams, and selectively irradiatingthe sub-beams onto an amorphous semiconductor on a substrate, whereinlaser beams emitted by a plurality of laser sources are simultaneouslyirradiated onto the semiconductor and a difference between divergingangles of the plurality of laser beams is corrected.

Also, an apparatus for crystallizing a semiconductor, according to thepresent invention, comprises at least one laser source, beam dividingmeans for dividing a laser beam emitted by the laser source into aplurality of sub-beams, at least one focussing optical system forfocusing the sub-beams on an amorphous semiconductor on a substrate, amoving mechanism for changing a distance between at least two spotpositions of the sub-beams formed by the focussing optical system, firstmirrors for directing a laser beam to the focussing optical system, andsecond mirrors provided in the focussing optical system to receive thesub-beams reflected by the first mirrors, wherein the sub-beams betweenthe first mirrors and the second mirrors are parallel to a direction ofmovement of the moving mechanism.

In these structures, throughput can be improved by simultaneouslyirradiating a plurality of sub-beams. In the display region of thedisplay device, the TFT portions are limited compared to the surfacearea of the pixels so, in light of the fact that it is not necessary tocrystallize the entire display region, throughput can be furtherincreased by selectively irradiating the sub-beams onto only thoseportions that must be crystallized. Although those portions that are notirradiated by the beam remain an amorphous semiconductor, they areeliminated when the TFTs are separated and, therefore, they pose noproblem if they are left as amorphous semiconductors.

Next, a method for crystallizing a semiconductor, according to thepresent invention, comprises the step of irradiating laser beams emittedby a plurality of laser sources onto a semiconductor layer on asubstrate through a focussing optical system to melt and crystallize thesemiconductor layer, wherein the plurality of laser beams are irradiatedonto the substrate without overlap, scan the semiconductor layer inparallel to each other, and are positioned so that their molten tracksoverlap each other.

Also, a method for crystallizing a semiconductor, according to thepresent invention, comprises the step of irradiating laser beams emittedby a plurality of laser sources onto a semiconductor layer on asubstrate through a focussing optical system to melt and crystallize thesemiconductor layer, wherein a plurality of beam spots formed by thelaser beams emitted by the laser sources at least partially overlap eachother.

Further, an apparatus for crystallizing a semiconductor, according tothe present invention, comprises first and second laser sources, afocussing optical system, and a combining optical system for guidinglaser beams emitted by the first and second sources to the focussingoptical system, wherein the combining optical system comprises a λ/2plate disposed after the first laser source, a beam expander disposedafter at least one of the first and second laser sources, and apolarizing beam splitter for combining laser beams emitting by the firstand second laser sources.

In these structures, by irradiating laser beams emitted by the first andsecond laser sources onto an amorphous semiconductor on a substratethrough the focussing optical system, the irradiated beam spot can beincreased in size. By increasing the size of the beam spot, the meltwidth increases and, therefore, even if the necessary scan speed isconstant in order to attain high quality polysilicon, the area scanspeed is high. Hence, polysilicon of excellent quality can be attainedwith a high throughput.

Next, an apparatus for crystallizing a semiconductor, according to thepresent invention, comprises a laser source, a stage for supporting asubstrate including an amorphous semiconductor, and an optical focussingsystem, wherein the stage comprises a plurality of first stage membersdisposed in parallel and movable simultaneously in a first direction, asecond stage member disposed above the first stage members and movablein a second direction perpendicular to the first direction, and a thirdstage member rotatably disposed above the second stage member, whereby alaser beam emitted by the laser source is irradiated onto asemiconductor on a substrate fixed to the third state member through theoptical focusing system to melt and crystallize the semiconductor.

In this structure, in the stage for supporting the substrate includingthe amorphous semiconductor, a plurality of first stage members aredisposed at the lowermost position and support the second stage memberand the third stage member. The second stage member can be moved at highspeed. Consequently, it is not necessary for the high speed movablesecond stage member to support the plurality of first stage members, andtherefore the load thereon is small. The plurality of first stagemembers move simultaneously and support the second stage member withoutbending, which is long, because it moves at high speed. Accordingly, thesecond stage member can be a high-speed member and the crystallizationthroughput can be improved.

Also, a method for crystallizing a semiconductor, according to thepresent invention, comprising the step of irradiating a laser beam ontoa semiconductor on a substrate having a display region and a peripheralregion around the display region to melt and crystallize thesemiconductor, performing crystallization of the peripheral region in afirst scanning direction, after rotating a rotatable stage supportingthe substrate by 90 degrees, performing crystallization of theperipheral region in a second scanning direction perpendicular to thefirst scanning direction, and performing crystallization of the displayregion in a third scanning direction parallel to a direction along whichsub-pixel regions of the three primary colors of pixels are arranged.

In this structure, crystallization of the peripheral region andcrystallization of the display region can be continuously performed, andoverall crystallization throughput can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be more fully understood from the descriptionof preferred embodiments of the invention set forth below, together withthe accompanying drawings, wherein:

FIG. 1 is a schematic sectional view showing a liquid crystal displaydevice according to an embodiment of the present invention;

FIG. 2 is a schematic plan view showing a glass substrate of FIG. 1;

FIG. 3 is a schematic plan view showing a mother glass for making theglass substrate of FIG. 2;

FIG. 4 is a flowchart showing the process of forming the TFTs on theglass substrate and the TFTs of the peripheral region;

FIG. 5 is a flowchart showing the content of the crystallizing step ofFIG. 4;

FIG. 6 is a perspective view showing an example of selectivelyirradiating the amorphous silicon layer in the display region on theglass substrate with sub-beams;

FIG. 7 is a view showing the optical device for adjusting the beam spotof the sub-beam;

FIG. 8 is a view showing the CW laser oscillators and a sub-beamselective irradiation system;

FIG. 9 is a view showing a sub-beam selective irradiation system formingsixteen sub-beams;

FIG. 10 is a plan view showing a specific example of the sub-beam focusassembly of FIG. 9;

FIG. 11 is a front view showing the sub-beam focus assembly of FIG. 10;

FIG. 12 is a side view showing the sub-beam focus assembly of FIG. 10;

FIG. 13 is a view showing the relationship between the sub-beams and thescan pitch;

FIG. 14 is a view showing the relationship between two glass substratesand a plurality of sub-beams;

FIG. 15 is a view showing an example of an arrangement of sub-beams;

FIG. 16 is a view showing an example of an arrangement of sub-beams;

FIG. 17 is a view showing a TFT arrangement and laser scanning in orderto explain the principle of the present invention;

FIG. 18 is a view showing a modified example of the sub-beam assembly ofFIGS. 8 to 12;

FIG. 19 is a view illustrating a prior art crystallizing method with anexcimer pulse laser;

FIG. 20 is a view illustrating a prior art crystallizing method with aCW laser;

FIG. 21 is a perspective view showing a step of crystallizing asemiconductor layer by means of a laser beam according to a furtherembodiment of the present invention;

FIG. 22 is a view showing a laser device used in crystallizing thesemiconductor of the peripheral region;

FIG. 23 is view showing a modified example of the laser device;

FIG. 24 is a view showing an example of beam spots;

FIG. 25 is a view showing an example of beam spots;

FIG. 26 is a view showing a step of crystallizing a semiconductor layerby means of a laser beam according to a further embodiment of thepresent invention;

FIG. 27 is a perspective view showing a movable stage supporting a glasssubstrate having an amorphous silicon layer thereon;

FIG. 28 is a view showing the operation of a laser scan; and

FIG. 29 is a perspective view showing a prior art movable stage.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be explained hereunder withreference to the drawings.

FIG. 1 is a schematic sectional view showing the liquid crystal displaydevice according to an embodiment of the present invention. The liquidcrystal display device 10 comprises a pair of opposing glass substrates12 and 14 and a liquid crystal 16 inserted therebetween. Electrodes andalignment layers can be provided on the glass substrates 12 and 14. Oneof the glass substrates 12 is a TFT substrate, and the other glasssubstrate 14 is a color filter substrate.

FIG. 2 is a schematic plan view showing the glass substrate 12 ofFIG. 1. The glass substrate 12 has a display region 18 and a peripheralregion 20 around the display region 18. The display region 18 includes alarge number of pixels 22. In FIG. 2, one pixel 22 is shown in a partialenlargement. The pixel 22 includes three primary color sub-pixel regionsR, G and B, and a TFT 24 is formed in each of the sub-pixel regions R, Gand B. The peripheral region 20 has TFTs (not shown), the TFTs in theperipheral region 20 being arranged more densely than the TFTs 24 of thedisplay region 18.

The glass substrate 12 of FIG. 2 forms a 15″ QXGA liquid crystal displaydevice and has 2048×1536 pixels 22. 2048 pixels are arranged in thedirection in which the three primary color sub-pixel regions R, G and Bare arranged (horizontally), so that the number of sub-pixel region R. Gand B is 2048×3. 1536 pixels are arranged in a direction perpendicular(vertically) to the direction in which the three primary color sub-pixelregions R, G and B are arranged (horizontally). In the process of thesemiconductor crystallization, laser scanning is performed in directionsparallel to sides of the peripheral region 20, and laser scanning iscarried out in the display region 18 in the directions indicated by thearrows A and B.

The reason for this is that, because the TFTs 24 are densely arranged inthe direction of the arrows A and B and sparsely arranged in thedirection perpendicular to the direction of the arrows A and B, and onthe mother glass, which is substantially square, the number of laserscans required in the A/B direction is less, therefore throughput ishigher.

FIG. 3 is a schematic plan view showing a mother glass 26 for making theglass substrate 12 of FIG. 2. The mother glass 26 encompasses aplurality of the glass substrates 12. In the example shown in FIG. 3,one mother glass 26 includes four glass substrates 12, but one motherglass 26 can include more than four glass substrates 12.

FIG. 4 is a flowchart showing the process of forming the TFTs 24 of theglass substrate 12 and the TFTs of the peripheral region 20. In step S1,an insulating layer and an amorphous silicon layer are formed on theglass substrate. In step S2, the amorphous silicon layer is crystallizedto form polysilicon. In step S3, the TFTs are separated, leaving thenecessary silicon portions such as those silicon portions that are tobecome TFTs and the like, and eliminating the unnecessary polysiliconand amorphous silicon layer portions. In step S4, gate electrodes, drainelectrodes, interlayer insulating layers, and contact holes are formed.In step S5, an insulating layer and an ITO layer are formed, and theglass substrate 12 is completed. The ITO layer becomes pixel electrodesfor forming the pixels 22.

FIG. 5 is a flowchart showing the content of the crystallization step S2of FIG. 4. A CW laser (continuous wave laser) oscillator 30 is used inthe crystallization step S2. The laser beam output from the CW laseroscillator 30 is supplied to a peripheral region irradiation system 32and a sub-beam selective irradiation system 34 one after another.Firstly, the laser beam is focussed and irradiated onto the amorphoussilicon of the peripheral region 20 of the glass substrate 12 to meltand harden the amorphous silicon to crystallize it into a polysilicon.Then, the sub-beam is selectively focussed and irradiated onto theamorphous silicon 36 of the display region 18 of the glass substrate 12to melt and harden the amorphous silicon to crystallize it into apolysilicon.

Since the TFTs of the peripheral region 20 are arranged more denselythan the TFTs 24 of the display region 18, high quality polysilicon isrequired in the peripheral region. In the peripheral region irradiationsystem 32, the peripheral region 20 is irradiated with a relatively highpower laser beam from the CW laser oscillator 30 at a relatively lowscan speed. If used in the example described above, scanning isperformed with a beam width of 250 μm and a scanning speed of 40 cm/s,giving an area scan speed of 1 cm²/s.

On the other hand, as the TFTs 24 of the display region 18 do notrequire polysilicon of higher quality, in the sub-beam selectiveirradiation system 34, a laser beam from the CW laser oscillator 30 isdivided into sub-beams, to be described later, and the display region 18is irradiated by these sub-beams at a relatively high scanning speed. Bythis means, the overall throughput is improved and high qualitypolysilicon is attained in the regions that require it.

FIG. 6 is a view showing an example of selectively irradiating theamorphous silicon layer of the display region 18 on the glass substrate12 with a plurality of sub-beams SB emitted by the sub-beam selectiveirradiation system 34. The plurality of sub-beams SB are divided fromlaser beam output from the CW laser oscillator 30 to form beam spots atpredetermined intervals. Numeral 36 denotes the amorphous silicon layerformed on the glass substrate 12, and the glass substrate 12 is fixed toa XY stage 38 by means of a vacuum chuck of the XY stage.

The sub-beams SB are arranged so as to form beams spots in stripe-shapedportions 40 on the amorphous silicon layer 36 that includes positionswhere TFTs 24 are to exist, and the XY stage 38 moves (scans) in thedirections of the arrows A and B. The remaining stripe-shaped portions42 of the amorphous silicon layer 36 are not irradiated. That is, thestripe-shaped portions 40 of the amorphous silicon layer 36 areselectively irradiated with the sub-beams SB.

FIG. 7 is a view showing the optical system for adjusting the beam spotsof the sub-beams SB. This optical system comprises a mirror 44 fordiverting the optical path of the sub-beam SB, a substantiallysemicircular cylindrical lens 46, a substantially semicircularcylindrical lens 48 arranged perpendicularly to the lens 46, and aconvex lens 50. By means of this optical system, the beam spot of thesub-beam SB is formed into ellipses.

FIG. 8 is a view showing a plurality of CW laser oscillators 30 and 30a, and the sub-beam selective irradiation systems 34. A half-mirror 51is arranged in front of the CW laser oscillator 30 so that the laserbeam LB emitted by the CW laser oscillator 30 is divided into twosub-beams SB by the half-mirror 51. One sub-beam SB passing through thehalf-mirror 51 is further divided into two sub-beams SB by anotherhalf-mirror 52. Numeral 53 indicates a mirror. The other sub-beam SBreflected by the half-mirror 51 is further divided into two sub-beams SBby another half-mirror 54. In this manner, the laser beam LB emitted bythe CW laser oscillator 30 is divided into four sub-beams SB.

An independently adjustable shutter 55 and an independently adjustableND filter 56 are arranged in each of the optical paths of the sub-beamsSB. The shutters 55 can interrupt the sub-beams SB as necessary. The NDfilters 56 can adjust the power of the sub-beams SB.

Further, mirrors 57 are arranged in order to divert the horizontalsub-beams SB upwards in a vertical direction, and mirrors 58 arearranged in order to divert the vertical sub-beams SB sideways in ahorizontal direction. The mirrors 58 divert the sub-beams SB parallel tothe glass substrate 12 at different heights. The horizontal sub-beams SBare diverted downwards in a vertical direction by focussing units 59,condensed by the focussing units 59, and irradiated onto the amorphoussilicon layer 36 in predetermined beam spots.

Each focussing unit 59 includes the mirror 44, the lens 46, the lens 48and the convex lens 50 shown in FIG. 7, these optical components formingone unit. The focussing units 59 are movable within an allowable rangein the direction indicated by the arrow C. Beam profilers 60 arearranged on the optical axis on each of the focussing units 59. The beamprofilers 60 correct the focus positions of the respective sub-beams SB.Also, the beam profilers 60 can detect the focus positions of therespective sub-beams SB.

Between the half-mirror 51 and the ND filters 56, the four sub-beams SBare arranged at equal intervals parallel to each other within ahorizontal plane parallel to the glass substrate 12. Between the mirrors57 and the focussing units 59, the sub-beams SB are arranged at equalintervals parallel to each other within a vertical plane perpendicularto the glass substrate 12. The glass substrate 12 having the amorphoussilicon layer 36 is moved (scanned) in the direction A/B perpendicularto this vertical plane.

The area scan speed in the sub-beam selective irradiation system 34 isdefined by the number of sub-beams x the scan speed x intervals betweenthe stripe-shaped portions 40 of the amorphous silicon layer 36. Forthis reason, it is preferable to divide the laser beam LB into aplurality of sub-beams SB, and to increase the number of laseroscillators 30, so that sufficient power necessary for crystallizationis provided and the number of sub-beams is increased.

In FIG. 8, another laser oscillator 30 a is arranged parallel to thelaser oscillator 30 and, with this laser oscillator 30 a, opticalcomponents (half-mirrors, mirrors, focussing units, and the like, notshown in the drawing) identical to the optical components belonging tothe laser oscillator 30 are provided, so that it can form a further foursub-beams SB. In this case, eight sub-beams SB are all arranged at equalintervals parallel to each other within the same horizontal plane.

A beam expander 79 is arranged between the laser oscillator 30 a and thefirst half-mirror 51 a. The beam expander 79 adjusts the diverging angleof the laser beam LB. In other words, if there is an inconsistencybetween the diverging angles of the simultaneously radiated plurality oflaser beams LB of the laser oscillators 30 and 30 a, there is a case inwhich one laser beam LB (sub-beam SB) is focussed by the focussingoptical system, the focus of the other laser beam LB (sub-beam SB) willnot match, and therefore, by adjusting the diverging angle of the laserbeam LB, the focuses of both of the laser beams LB will match. The beamexpander 79 may also be arranged in the optical path of the other laserbeam LB. Also, two of them can be arranged as one in each of the opticalpaths of both laser beams LB.

FIG. 9 is a view showing a sub-beam selective irradiation system 34adapted to form sixteen sub-beams SB. This sub-beam selectiveirradiation system 34 includes four laser oscillators 30, two sub-beamdividing assemblies 62, and two sub-beam focussing assemblies 64. Two ofthe laser oscillators 30 corresponding to the two laser oscillators 30and 30 a of FIG. 8. One sub-beam dividing assembly 62 divides laserbeams LB output from two of the laser oscillators 30 and 30 a into eightsub-beams SB, and includes the optical components corresponding to thosearranged between the half-mirror 51 and the ND filters 56 of FIG. 8. Onesub-beam focussing assembly 64 is optically connected to one sub-beamdividing assembly 62, and includes the optical components correspondingto those from the mirrors 57 to the focussing units 59 of FIG. 8.

FIG. 10 is a plan view showing a specific example of the sub-beamfocussing assembly 64 of FIG. 9, FIG. 11 is a front view showing thesub-beam focussing assembly 64 of FIG. 10, and FIG. 12 is a side viewshowing the sub-beam focussing assembly 64 of FIG. 10. In FIG. 10 toFIG. 12, eight mirrors 57 and 58 and eight focussing units 59 aremounted to a frame 64F. Each focussing unit 59 is attached to the frame64F by means of an electrically driven stage 59S, and is movable withinan allowable range in the direction indicated by the arrow C in FIG. 8.

Where the peripheral region irradiation system 32 of FIG. 5 is used, theoptical components from the half-mirror 51 to the focussing unit 59 ofFIG. 8 are removed and optical components of the peripheral regionirradiation system 32 are set in the position of the half-mirror 51.

In the above structure, the intervals of the TFTs 24 is equal to thepitch of the pixels 22. According to the present invention, the areascan speed is improved in proportion to the pixel pitch and the numberof sub-beams. Also, the smaller the size of the TFTs 24, the more thesurface area that requires melting can be reduced, therefore the numberof sub-beams can be increased. Under the condition that the pixel pitchdoes not need to be excessively reduced, as far as the display be seenby the human eye, the size of the TFTs 24 can be reduced with advancesin miniaturization techniques. As a result, crystallization can beselectively performed only on those portions where it is necessary,without supplying energy to areas that do not require it, so thethroughput of the crystallization process can be improved, and anenergy-saving process can be realized.

In an example, the size of the TFTs 24 is such that a channel length isapproximately 4 μm and a channel width is approximately 5 μm. Thefluctuation of the XY stage that can perform high-speed scanning at 2m/s is in the order of a maximum of ±10 μm, and therefore the width ofthe sub-beams SB is at least 25 μm, and preferably 30 μm, with theconsideration of allowance for other factors. The need for increasingthe channel width can be easily achieved by the layout in which thechannel width is arranged parallel to the scanning direction.

The melt width (the width at which the stripe portions 40 of theamorphous silicon layer 36 are melted) changes according to the scanningspeed, the thickness of the silicon, the laser power, irradiationfocusing lenses, and the like. In the case where the depth of theamorphous silicon layer 36 is 150 nm and an optical system with thelenses of F=200 mm and F=40 mm in combination, that can attain anelliptical beam spot, is used, and laser scanning is performedperpendicular to the long axis of the ellipse, an effective melt widthof 30 μm can be attained. Consequently, even with the power lossaccompanied by the division of the laser beam LB, if 2W or more powercan be supplied to the divided sub-beams SB, the necessary melt width of30 μm can be maintained. The laser used is a Nd:YV04 continuous wavesolid laser.

With respect to 10W laser oscillation, the laser power values afterdivision into four sub-beams are 2.3W, 2.45W, 2.45W and 2.23W, all over2W. It is believed that the deviation in power values of ten to twentypercent of the sub-beams SB is due to deviation in the characteristicsof the mirrors and half-mirrors. Due to these values, power at the NDfilter 56 is somewhat attenuated, so that the power values of the foursub-beams SB are all a uniform 2.2W.

In FIG. 9, the 16 sub-beams SB are power adjusted by the ND filters 56so that all 16 sub-beams SB are adjusted to have the same power value of2.1W. Because the diverging angles of the beams from different laseroscillators differ, the focussing positions also differ, so in order tocorrect this, the beam expander is provided immediately after the laserbeam output from the laser oscillator and, by correcting the divergingangle thereof, the same focus positions can be attained. However, if thedislocation of a focus position does not differ significantly, a meltwidth of the same size can be achieved and no significant problems arecaused even if crystallization is performed with the focus positiondislocated.

In the glass substrate 12 of FIG. 2, the width of the peripheral regionsis approximately 2 mm.

Crystallization is performed using 16 sub-beams SB on the glasssubstrate 12 of a 15″ QXGA display device. The size of the pixels 22 is148.5 μm square. Consequently, the RGB sub-pixel size is 148.5 μm×49.5μm. In order to reduce the number of scans and increase overallthroughput, scanning is performed perpendicular to the side of 148.5 μm(the direction along which the RGB sub-pixels are arranged). Thearrangement of the 16 sub-beams SB at 148.5 μm intervals is not possibledue to the size of the optical system. The irradiating lenses of each ofthe focussing units 59 are arranged at intervals of 30 mm, and aremovable within the range of ±4 mm by means of the electrically drivenstage 59S with respect to the direction in which they are arranged.

As 30 mm/148.5 μm=202.02, a row of 202 TFTs 24 (the stripe portions 40of the amorphous silicon layer 36) exists between two focussing units59.

The interval between the first, endmost irradiating lens and the secondirradiating lens is consequently 202×148.5 μm=29997 μm=30000−3.

The interval between the first, endmost irradiating lens and the thirdirradiating lens is 202×148.5 μm×2=59994 μm=30000×2−6.

The interval between the first, endmost irradiating lens and the fourthirradiating lens is 202×148.5 μm×3=89991 μm=30000×3−9.

The interval between the first, endmost irradiating lens and the fifthirradiating lens is 202×148.5 μm×4=119988 μm.

The interval between the first, endmost irradiating lens and the sixthirradiating lens is 202×148.5 μm×5=149985 μm.

The interval between the first, endmost irradiating lens and the seventhirradiating lens is 202×148.5 μm×6=179982 μm.

The interval between the first, endmost irradiating lens and the eighthirradiating lens is 202×148.5 μm×7=209979 μm.

The interval between the first, endmost irradiating lens and the ninthirradiating lens is 202×148.5 μm×8=239976 μm.

The interval between the first, endmost irradiating lens and the tenthirradiating lens is 202×148.5 μm×9=269973 μm.

The interval between the first, endmost irradiating lens and theeleventh irradiating lens is 202×148.5 μm×10=299970 μm.

The interval between the first endmost irradiating lens and the twelfthirradiating lens is 202×148.5 μm×11=329967 μm.

The interval between the first, endmost irradiating lens and thethirteenth irradiating lens is 202×148.5 μm×12=359964 μm.

The interval between the first, endmost irradiating lens and thefourteenth irradiating lens is 202×148.5 μm×13=389961 μm.

The interval between the first, endmost irradiating lens and thefifteenth irradiating lens is 202×148.5 μm×14=419958 μm.

The interval between the first, endmost irradiating lens and thesixteenth irradiating lens is 202×148.5 μm×15=449955 μm=30000×15−45.

Accordingly, each irradiating lens is finely adjusted from a designedaverage position to 3 μm in the minus direction in the case of thesecond irradiating lens, 6 μm in the minus direction for the thirdirradiating lens, . . . , 45 μm in the minus direction for the sixteenthirradiating lens. Thus, the sub-beams are focused on the respective TFTregions. In this state, the sub-beams are irradiated with the output ofthe laser oscillators 30 of 10W and the scanning speed of 2 m/s.Irradiation is performed with each sub-beam SB of the power of 2W.

FIG. 13 is a view showing the relationship between the sub-beams SB andscan intervals. As shown in FIG. 13, the sub-beams SB are arranged atintervals “a”, which is (3 mm−3 μm). The interval between TFTs 24, i.e.the scan interval “b”, is 148.5 μm. Scanning is performed while the XYstage 38 is moved reciprocally in the direction indicated by the arrowsA and B. In other words, after the XY stage 38 moves in the direction ofthe arrow A, the XY stage then moves 148.5 μm in the directionperpendicular to the arrows A and B, then moves in the direction of thearrow B, then again moves 148.5 μm in the direction perpendicular to thearrows A and B. This operation is repeated. In FIG. 13, although each ofthe sub-beams SB is shown as scanning four times, in the example beingexplained here, each sub-beam SB scans 202 times.

In one scan in one scanning direction, the 16 sub-beams SB crystallizestripe portions 40 of the amorphous silicon layer 36 at the interval for202 pixels. Next, in the reverse scan, the 16 sub-beams SB crystallizethe adjacent stripe portions 40 of the amorphous silicon layer 36 at theinterval for 202 pixels. In 101 reciprocal scans (i.e. 202 scans),portions corresponding to 202×16=3332 pixels can be scanned. In thiscase, the area scan speed is 148.5 μm×2 m/s=47.5 cm²/s.

However, in the glass substrate 12 in this example, the number of pixelsin the vertical direction is only 1536. Consequently, in the nextexample to be explained, not 16, but rather 8 sub-beams SB are used.Since 1536=202×7+122=122×8+80×7, scanning is performed 122 times witheight beams, with the remaining 80 scans performed by seven sub-beamsSB. In this case, the eighth sub-beam SB is cut off by the shutter 55after the 122nd scan.

Since, in this example, the device has 16 sub-beams SB, as well asscanning and crystallizing one glass substrate 12 with eight sub-beamsSB, scanning and crystallization of the adjacent glass substrate 12 onthe mother glass 26 (FIG. 3) can be performed by the remaining eightsub-beams SB. However, in order to do this, it is preferable that thedistance between the end of the pixels of the current glass substrate 12and the nearest end of the pixels of the adjacent glass substrate 12 bean integral multiple of the pixel pitch. Alternatively, the positions ofthe pixels 22 of all of the glass substrates 12 on the mother glass 26are preferably arranged on a mesh having a uniform pixel pitch.

FIG. 14 is a view showing the relationship between two glass substrates12 a and 12 b on the mother glass 26 and a plurality of sub-beams SB8and SB9. Sub-beam SB8 is the eighth sub-beam SB among eight sub-beams SBfor crystallizing the glass substrate 12 a, and sub-beam SB9 is thefirst sub-beam SB among eight sub-beams SB for crystallizing the glasssubstrate 12 b.

When the eighth sub-beam SB8 has finished 122 scans, it is stopped bythe shutter 56. The length of the scan region of the remaining 80 scanswhich the eighth sub-beam SB8 is capable of scanning is 148.5μm×80=11.880 mm. If this distance is the same as the distance betweenthe last pixel of the glass substrate 12 a and the first pixel of theadjacent glass substrate 12 b, the ninth to sixteenth sub-beams SB canbe used to crystallize the adjacent glass substrate 12 b withoutwastage. In other words, when the first sub-beam SB scans the firstpixels of the glass substrate 12 a, the ninth sub-beam SB scans thefirst pixels of the glass substrate 12 b. Where the peripheral region 20of 2 mm of the glass substrate 12 exists, the gap (L) of(11.880−2×2=7.88 mm) can be provided between the two glass substrates 12a and 12 b.

In the present apparatus, as the movable region of ±4 mm relative to theaverage position is provided for each sub-beam SB, irregularities thatcan be canceled by this movable range can be accommodated, but the needof adjustment relative to the adjacent glass substrate one by one iscomplicated, and this process is time-consuming, so it is preferable forthe positions of the pixels of all of the panels of the mother glasssubstrate to be arranged on a mesh having a uniform pixel pitch.

FIG. 14 shows an imaginary mesh M at the pixel pitch of the pixels onthe mother glass. Designing the mother glass so that the arrangement ofthe pixels on the plurality of glass substrates 12 a and 12 b is thesame as the imaginary mesh M, which is drawn with the pixel pitch of themother glass, is preferred.

Stopping this type of single sub-beam SB temporarily occurs due to itsrelationship to the pixel pitch, the size of the glass substrates 12,the average positions of the sub-beams SB, and the number of sub-beamsSB. In the case of a large glass substrate 12, it should be clear that16 sub-beams SB can be used more effectively.

FIG. 15 is a view showing an example of the arrangement of the sub-beamsSB. To increase effectiveness, it is preferable to reduce the pitchbetween sub-beams SB. However, because of the limit to which the lensesand mirrors can be miniaturized, there is a limit to which the pitch ofthe sub-beams SB can be reduced. Under this limitation, in order toreduce the pitch, the sub-beam SB irradiating system can be arranged innot one row, but a plurality of rows as shown in FIG. 15, at the sameintervals but staggered. Arranging the system in a plurality of rows inthis manner, the distance at which the XY stage can move at a uniformhigh speed increases at the same rate that the number of rows increasesover the width of the mother glass, therefore throughput decreasessomewhat.

FIG. 16 is a view showing an example of the sub-beam SB arrangement. Inovercoming this problem in two rows, although arranging the sub-beamirradiating system of the two rows by displacing the positions of bothsub-beams SB is the same, this can also be achieved by arranging eachrow in the foremost position of the mother glass when the stage hasfinished moving at a uniform high speed, as shown in FIG. 16. Naturally,the sub-beam irradiating systems of a plurality of rows can also bearranged at these positions.

FIG. 17 is a view explaining the principle of the present invention.FIG. 18 is a view showing modified example of the sub-beam focussingassembly of FIGS. 8 to 12.

When annealing the panel surface of the amorphous silicon panel bylaser, if the entire panel surface is annealed all over, too much timeis required. If the TFTs 24 are sporadically scattered as in FIG. 17, itis permissible to anneal only the stripe portions 40 that include theTFTs 24, and there is no need to anneal the entire surface.

In scanning to anneal the panel surface by laser beam, there are amethod of moving the laser beams (sub-beams) while the panel is fixed,and a method of moving the panel while the laser beams (sub-beams) arefixed. The present invention can be applied to either method.

As the laser annealing with a single laser beam takes too much time, itis desired to increase the number (n) of the laser beams, so that “n”laser beams lead to 1/n time, and therefore a plurality of laser beams(n beams) are used. As shown in FIG. 17, the TFTs 24 are regularlyarranged at pitch PTR, but this pitch PTR varies according to theproducts. The apparatus of the present embodiment can be adapted fordifferent pitches.

This is illustrated further in FIG. 18. Where annealing with a plurality(four in FIG. 18) of laser beams (sub-beams SB), the panel must beirradiated with sub-beams SB at equal intervals. This mechanism will beexplained using the four beam example of FIG. 18.

The four sub-beams SB are turned 90 degrees using optical pathconversion mirrors 58, so that the sub-beams SB run parallel to thedirection of movement C of the stage shown in the drawing (left-rightmovement in FIG. 18). Next, the sub-beams SB are turned 90 degrees usingoptical path conversion mirrors 44, so that the sub-beams SB passthrough the exact center of the lens units LU shown in the drawing(lenses 46, 48 and 50 in FIG. 7). The mirrors 44 and lens units LU arelocated in the focussing units 59. The focussing unit 59 is mounted onthe guide 59G (manual stage) and the electrically driven stage 59S, sothat when the electrically driven stage 59S moves (left-right movementin the drawing), the entire focussing unit 59 moves left or right. Whenthe electrically driven stage 59S moves (left-right movement in thedrawing), the entire focussing unit 59 moves left or right, so that thelaser beam (sub-beam SB) always passes through the exact center of thelens unit LU.

With this mechanism, the interval between the outgoing laser beampassing through the lens unit LU and the next outgoing laser beampassing through the next lens unit LU (laser beam pitch PLB1) can beadjusted. The interval between other laser beams can be similarlyadjusted using the same method as for the laser beam pitch PLB1.

Next, the method of annealing the panel surface having TFTs at thetransistor pitch PTR as shown in FIG. 17 with a plurality of (four inFIG. 18) laser beams (sub-beams SB) having the structure of FIG. 18,without waste or loss will be described.

The transistor pitch PTR is usually in the order of 100 μm (this differsaccording to the product being produced, as already been described). Forexample, the case where the PTR is 90 μm and the initial laser beampitch is 20 mm will be specifically described. As 20 mm/90 μm=222.22 . .. , the integer 222 is attained by rounding off. 222×90 μm=19.98. Thus,if the laser beam pitches PLB1 to PLB4 are made 19.98 mm, fourtransistor rows with a laser pitch of 19.98 mm can be annealed in onescan. Next, after moving the panel with respect to the laser beam group90 μm perpendicularly to the laser scanning direction, and againperforming a laser scan, the next four transistor rows can be annealed.When laser scanning is thereafter performed another 220 times (scanninghas already been performed twice, thus the total number of scans is222), 222×4 transistor rows are annealed without duplication or loss. Aregion of 222×4×90 μm=19.98 mm×4=approximately 80 mm can be annealedwithout waste or failure. Next, after moving the panel with respect tothe laser beam group 80 mm perpendicularly to the laser scanningdirection, if annealing is performed by the same procedure, a panel ofany size can be annealed without duplication or loss.

The present embodiment provides a means for annealing without waste orloss even when laser annealing a panel having a variety of transistorpitches, by setting the laser beam pitch at an integral multiple of thetransistor pitch with a structure that can adjust the laser beam pitch.A system of using a plurality of laser beams when laser annealing anamorphous silicon panel or the like using a laser has already beenproposed. The present embodiment provides a method that can anneal usinga plurality of laser beams and can respond to transistor pitches thatvary according to the product and are scattered on the surface of thepanel, and by arranging the interval between a plurality of laser beamsat an integral multiple of the transistor pitch, provides a means thatcan anneal effectively and without waste.

As explained above, according to the present invention, throughput canbe increased even when using a CW solid laser.

Next, a further embodiment of the present invention will be explained.This embodiment includes the fundamental features described withreference to FIGS. 1 to 4.

FIG. 21 is a view showing a step of crystallizing an amorphous siliconlayer (semiconductor layer) by means of a laser beam. The amorphoussilicon layer 36 is formed on a glass substrate 12 with an insulatinglayer of SiO₂ or the like arranged therebetween, and the glass substrate12 is fixed to an XY stage 38 by a vacuum chuck or a mechanical stopperof the stage 38. A laser beam LB is irradiated onto the amorphoussilicon layer 36, and the XY stage 38 is moved in a predetermineddirection, so that scanning is performed. Initially, the laser beam isfocussed and irradiated onto the amorphous silicon layer 36 of theperipheral region 20 of the glass substrate 12, to melt and harden theamorphous silicon layer to crystallize the amorphous silicon layer intopolysilicon. Then, the laser beam is focussed and irradiated onto theamorphous silicon layer 36 of the display region 18 of the glasssubstrate 12, to melt and harden the amorphous silicon layer tocrystallize the amorphous order of operation silicon layer intopolysilicon. The reason for this is that, in the case where the laserscanning is performed in an intersecting manner, the crystallinity ofthe intersecting portions when crystallization is performed firstly witha strong laser light corresponding to that as for the peripheral regionand then with a weak laser light corresponding to that for the displayregion is identical to the crystallinity of the peripheral region whenthe strong laser light is used, but the crystallization by the stronglaser light is insufficient if the laser light is irradiated in thereverse order. This is because light absorption is less if the amorphoussilicon is partially crystallized to a certain degree.

As the TFTs of the peripheral region 20 are arranged more densely thanthe TFTs 24 of the display region 18, high quality polysilicon isrequired. Consequently, laser scanning of the peripheral region 20 isperformed with a laser beam of relatively high power at a relatively lowscanning speed and, as the TFTs 24 of the display region 18 do notrequire polysilicon of a higher quality, scanning is performed with arelatively low power laser beam (or by sub-beams divided from the laserbeam) at a relatively high scanning speed.

FIG. 22 is a view showing a laser device 70 used for crystallizing thesemiconductor of peripheral region 20. The laser device 70 is used withthe XY stage 38 of FIG. 5 for crystallization. The laser device 70comprises two laser sources (continuous wave (CW) laser oscillators) 71and 72, a common focussing optical system 73, and a combining opticalsystem 74 for guiding laser beams LB outgoing from the two laser sources71 and 72 to the focussing optical system 73.

The focussing optical system 73 comprises a substantially semicircularcylindrical lens 75, a substantially semicircular cylindrical lens 76arranged perpendicular to the lens 75, and a convex lens 77. The beamspots of the laser beams LB are formed in the elliptical shape by thefocussing optical system 73.

The combining optical system 74 comprises a λ/2 plate 78 disposed afterthe first laser source 71, a beam expander 79 disposed after the secondlaser source 72, and a polarizing beam splitter 80 for combiningoutgoing laser beams LB from the first and second laser sources 71 and72. Numeral 81 denotes a mirror.

The laser beams LB outgoing from the laser sources 71 and 72 arecombined by the combining optical system 74, and are irradiated onto theamorphous semiconductor 36 of the glass substrate 12 through thefocussing optical system 73 to crystallize the amorphous semiconductor36. The beam expander 79 adjusts the diverging angle of the laser beamLB. In other words, if there is a deviation between the diverging anglesof the laser beams LB, there is a case where one laser beam LB isfocussed by the focussing optical system 73 but the focus of the otherlaser beam LB may not match, and therefore, it is intended that thefocusses of the two laser beams LB are matched, by adjusting thediverging angle of the laser beam LB by means of the beam expander 79.The beam expander 79 may also be arranged in the optical path of theother laser beam LB. Also, two beam expanders can be arranged in boththe optical paths of the laser beams LB.

The laser beams LB emitted by the first and second laser sources 71 and72 are vertically linearly polarized, and the laser beam LB emitted bythe first laser source 71 has its plane of polarization rotated 90degrees by the λ/2 plate 78 and is horizontally linearly polarized.Consequently, the laser beam LB output from the first laser source 71and passing through the λ/2 plate 78, and the laser beam LB output fromthe second laser source 72 are guided into the polarizing beam splitter80, and the two laser beams LB are directed to the amorphoussemiconductor 36 in a substantially superposed manner. The change in thestate of linear polarization is illustrated in more detail in FIG. 23.

Each laser beam LB passes through the focus optical system 73 to form anelliptical beam spot. As shown in FIG. 24, the individual beam spots ofthe laser beams LB are superposed, and the beam spots of the combinedlaser beams LB form a cocoon shaped beam spot BS. This can be achievedby slightly displacing the angle of any one of the mirrors 81, forexample. In other words, the laser beams LB outgoing from the of lasersources 71 and 72 form elliptical beam spots, respectively, and theelliptical beam spots mutually overlap in the direction of their longaxes.

In this example, the SiO₂ layer is formed at the thickness of 400 nm onthe glass substrate 12 by plasma CVD, and the amorphous silicon 36 isformed thereon by plasma CVD to a thickness of 100 nm. The laser used isa continuous wave Nd:YV04 solid laser. In one example, where a singlelaser source is used, a 400 μm×20 μm beam spot is formed at the laserpower of 10W. If scanning is performed using a single laser, with alaser width of 400 μm and a scan speed of 50 cm/s, the area scan speedof 200 cm²/s can be achieved. Also, within the laser irradiation widthof 400 μm, the 150 μm wide stripe portion of the amorphous semiconductor36 is well melted and crystallized, and exhibits a flow type grainboundary. Once the TFTs are formed in the polysilicon region made fromthis flow type grain boundary, a high mobility characteristic of 500(cm²/Vs) can be attained.

The combined beam spot of the laser beams outgoing from the two lasersources 71 and 72, as shown in FIG. 22, is 600 μm×20 μm. When the laserscan is performed at the laser power of 10W and the spot width of 600μm, scan speed of 50 cm/s, the 350 μm wide stripe portion of theamorphous semiconductor 36 is particularly well melted and crystallizedwithin the laser irradiation width of 600 μm, and attains a flow typegrain boundary. The high quality crystallized stripe portion with awidth of 350 μm is twice the width of the high quality crystallizedstripe portion with a width of 150 μm using a single laser. In otherwords, by means of the compound heating of the two beam spots, the beamspot size and effective melt width (high quality crystallization width)can be enlarged.

FIG. 23 is view showing a modified example of the laser device 70. Thelaser device 70A of FIG. 23 includes two units of optical system. Eachunit of optical system includes the same components as those of thelaser device 70 of FIG. 22. The optical system of the first unit usesthe same numbers as FIG. 22 to indicate the same optical components,with the subscript “a” attached, while the optical system of the secondunit uses the same numbers as FIG. 22 to indicate the same opticalcomponents, with the subscript “b” attached. The beam expander 79 can beprovided as appropriate.

The optical systems of the two units are arranged in close proximity,and the beam spots BS created by the optical systems of the two unitsare arranged so that they are shifted in both the directionperpendicular to and the direction parallel to the scanning direction.In this structure, each of 350 μm effective melt width regions isarranged so that the scan track overlaps by 50 μm and the effective meltwidth is 650 μm.

FIG. 25 is a view showing another example of beam spots. Three beamspots BS are arranged so that they are shifted in both the directionperpendicular to, and the direction parallel to, the scanning direction.The three beam spots are all irradiated onto the substrate, whileshifted in the scanning direction and without overlapping. However, thethree beam spots are arranged such that they scan the semiconductorlayer in parallel and overlap with each other when seen in the scanningdirection so that their melt widths overlap each other. Also, more thanthree beam spots can be arranged so that they are shifted in both thedirection perpendicular to, and the direction parallel to, the scanningdirection.

As explained above, according to the present invention, throughput canbe increased even when using a CW fixed laser.

Next, a further embodiment of the present invention will be explained.This embodiment includes the fundamental features described withreference to FIGS. 1 to 4. FIG. 26 is a view showing a step ofcrystallizing an amorphous silicon layer (semiconductor layer) 36 bymeans of a laser beam. The amorphous silicon layer 36 is formed on aglass substrate 12, with an insulating layer of SiO₂ or the liketherebetween, and the glass substrate 12 is fixed to a movable stage 38by a vacuum chuck or a mechanical stopper of the stage. A laser beam LBoutput from a laser source (continuous wave (CW) laser oscillator) 30passes through a concave lens 31, is reflected by a mirror 44, passesthrough a focussing optical system, and is irradiated onto the amorphoussilicon layer 36. The focussing optical system comprises a substantiallysemicircular cylindrical lens 46, a substantially semicircularcylindrical lens 48 arranged perpendicular to the lens 46, and a convexlens 50. The beam spot of the laser beam LB passing through the convexlens 50 is formed into an elliptical shape.

The laser beam LB is irradiated onto the amorphous silicon layer 36, andthe movable stage 38 is moved in a predetermined direction, so that thelaser scanning is performed. Firstly, the laser beam LB is focussed andirradiated onto the amorphous silicon 36 of the peripheral region 20 ofthe glass substrate 12, to melt and harden the amorphous silicon tocrystallize into polysilicon. Then, the laser beam is focussed andirradiated onto the amorphous silicon 36 of the display region 18 of theglass substrate 12 to melt and harden the amorphous silicon tocrystallize it into polysilicon.

As the TFTs of the peripheral region 20 are arranged more densely thanthe TFTs 24 of the display region 18, high quality polysilicon isrequired. Consequently, laser scanning of the peripheral region 20 isperformed with a laser beam of relatively high power at a relatively lowscanning speed and, as the TFTs 24 of the display region 18 do notrequire polysilicon of a higher quality, scanning is performed with arelatively low power laser beam (or by sub-beams divided from the laserbeam) at a relatively high scanning speed.

FIG. 27 is a perspective view showing the movable stage 38 supportingthe glass substrate 12 having the amorphous silicon layer 36. Themovable stage 38 comprises first stage members 38A arranged in paralleland moves in a first direction P, Q synchronously, a second stage member38B disposed above the first stage members 38A and moves in a seconddirection R, S perpendicular to the first direction, and a third stagemember 38C rotatably disposed above the second stage 38B. The thirdstage member 38C has a vacuum chuck 38D for securing the amorphoussemiconductor 36 of the glass substrate 12. The third stage member 38C(the rotatable stage) can rotate within the angular range of 110degrees.

In the movable stage 38, the first stage members 38A are disposed at thelowermost position and support the second stage member 38B and the thirdstage member 38C. The second stage member 38B is large and long, has agreater stroke, and can move at high speed. Consequently, the secondstage member 38B which is movable at high speed is not required tosupport the first stage members 38A, and therefore the load on thesecond stage member 38B is small. The first stage members 38A movesimultaneously and support the second stage member 38B without bending.Accordingly, the second stage member 38B can be driven at a higherspeed, by which the throughput of crystallization can be improved.

FIG. 28 is a view showing a laser scanning operation. Firstly, laserscanning of the peripheral region 20 is performed. In the laser scanningof the peripheral region 20, (1) crystallization of the areas of theperipheral region 20 running parallel to the first scanning direction P,Q is performed, (2) next, after the third stage member 38C (therotatable stage) supporting the glass substrate 12 is rotated 90degrees, crystallization of the areas of the peripheral region 20running parallel to the second scanning direction R, S perpendicular tothe first scanning direction P, Q is performed. Then, (3) the displayregion 18 is crystallized in a third scanning direction A, B parallel tothe direction in which sub-pixel regions of the three basic colors ofthe pixels 22 are arranged.

The reason for this order of operation is that, in the case where thecrystallizing scanning is performed over a plurality of panels andscanning intersecting portions occur, the crystallinity of theintersecting portions when crystallization is performed firstly with ahigh energy density laser light of the peripheral region and then with aweak laser light corresponding to that of the display region isidentical to that when the crystallization is performed with a stronglaser light, but the crystallization by the strong laser light isinsufficient if the laser light is irradiated in the reverse order. Thisis because the absorption of light is less if the amorphous silicon ispartially crystallized to a certain degree, compared to the amorphousstate. An additional reason for performing the operation in the order isthat scanning in the same direction can be continued.

That is, initially, laser scanning of two shorter sides among four sidesof the peripheral region 20 of the glass substrate 12 is performed, thenlaser scanning of two longer sides among four sides of the peripheralregion 20 of the glass substrate 12 is performed. In the scanning of thetwo shorter sides, the shorter sides of the glass substrate 12 arepositioned perpendicular to the second stage member 38B, and the secondstage member 38B is reciprocally moved in the first scanning directionP, Q together with the glass substrate 12. The second stage member 38Bis driven so as to move in one direction P, and while this movement, thesecond stage member 38B is accelerated from a stationary position, laserscanning is performed with the second stage member 38B in a constantspeed state, and the second stage member 38B is decelerated and stoppedafter it has passed the laser scanning region. Then, after the firststage members 38A is moved a minute amount in the directionperpendicular to the first scanning direction P, Q, the second stagemember 38B is driven so as to move in the opposite direction Q. At thattime, the second stage member 38B is accelerated, moves at a constantspeed, and is decelerated. While repeating this reciprocal movement,laser scanning is performed so that the end portions of the irradiatedregions overlap each other.

Subsequently, the third stage member 38C (rotatable stage) is rotated 90degrees and the long sides of the glass substrate 12 are positionedparallel to the second stage member 38B. Laser scanning of the two longsides is performed in the second scanning direction R, S. Scanning ofthe two long sides is performed while repeating the reciprocal movementin the same manner as for the short sides.

After this, laser scanning of the display region 18 is performed in thethird scanning direction A, B. As the third scanning direction A, B isparallel to the second scanning direction R, S, the third stage member38C (rotatable stage) is supported in the same rotational position asthat when the two long sides of the peripheral region 20 are scanned.After the first stage members 38A are moved to initial positions in thedirection perpendicular to the second scanning direction R, S, thesecond stage member 38B is driven so as to move reciprocally in thethird scanning direction A, B.

Between reciprocal movements of the second stage member 38B, the firststage members 38A are moved by a minute amount in the directionperpendicular to the second scanning direction R, S. The amount ofmovement of the first stage members 38A during laser scanning of thedisplay region 18 is greater than the amount of movement of the firststage members 38A during laser scanning of the peripheral region 20. Inother words, laser scanning of the display region 18 is performed at alarger pitch than that of laser scanning of the peripheral region 20.Also, laser scanning of the display region 18 is performed at a higherscanning speed than laser scanning for the peripheral region 20.Further, laser scanning of the display region 18 is performed at a lowerlaser power than laser scanning of the peripheral region 20. Furtherstill, the number of scans when crystallization of the display region 18is performed in the third scanning direction A, B, parallel to thedirection in which the three primary color sub-pixel regions of thepixels 22 are arranged, is significantly less than the number of scanswhen crystallization of the display region 18 is performed in adirection perpendicular to the direction in which the three primarycolor sub-pixel regions of the pixels 22 are arranged (perpendicular tothe direction A, B), therefore the laser scanning time can be shortened.

In this manner, by positioning the high precision first stage members38A at the bottom, and positioning the high speed second stage member38B thereabove, the weight of the load on the high speed second stagemember 38B can be reduced. Simultaneously, the long second stage member38B can be supported by the plurality of first stage members 38A so thatthe second stage member 38B can be supported without bending. Theplurality of first stage members 38A are driven in synchronization.Thus, when the high speed second stage member 38B is accelerated anddecelerated the acceleration can be increased and the time taken formovements other than for laser scanning can be shortened. By enablingthe third stage member 38C (rotatable stage) to rotate within the rangeof 110 degrees, after mounting the glass substrate 12 in the vacuumchuck 38D, crystallization of the peripheral region 20 andcrystallization of the display region 18 can be continuously performed.Thus, according to the present invention, the throughput ofcrystallization can be improved.

In the example, the SiO₂ layer is formed at a thickness of 400 nm on theglass substrate 12 by plasma CVD, and the amorphous semiconductor 36 isformed thereon by plasma CVD to a thickness of 100 nm. The laser used isa continuous wave Nd:YV04 solid laser. In one example, the laser is 10Wand forms a 400 μm×20 μm beam spot. If scanning is performed using asingle laser source, with a laser width of 400 μm and a scan speed of 50cm/s, an area scan speed of 200 cm²/s can be achieved. Also, within thelaser irradiation width of 400 μm, the 150 μm wide stripe portion of theamorphous semiconductor 36 is well melted and crystallized, and exhibitsa flow type grain boundary. Once the TFTs are formed in the polysiliconregion made from this flow type grain boundary, a high movementcharacteristic of 500 (cm²/Vs) can be attained.

As described above, according to the present invention, throughput canbe increased even in a case where a CW fixed laser is used.

1. An apparatus for crystallizing a semiconductor, comprising: first andsecond laser sources; a focussing optical system; and a combiningoptical system for guiding laser beams emitted by the first and secondlaser sources to the focussing optical system; wherein the combiningoptical system comprises a ½ plate disposed after the first lasersource, a beam expander disposed after at least one of the first andsecond laser sources, and a polarizing beam splitter for combining laserbeams emitted by the first and second laser sources.